Ointments Help Horses with Bug Bite Hypersensitivity

The results of a study conducted by a group of researchers from the Netherlands suggest that regular application of a topical ointment--medicated or nonmedicated--might provide some relief to horses suffering from insect bite hypersensitivity.

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The results of a study conducted by a group of researchers from the Netherlands suggest that regular application of a topical ointment--medicated or nonmedicated--might provide some relief to horses suffering from insect bite hypersensitivity (IBH).

Robin van den Boom, DVM, an assistant professor in the department of equine science at the University of Utrecht in Holland, and a group of colleagues recently completed a study in which they compared the results of treating horses with IBH using either a medicated plant-based (phytogenic) ointment or a placebo ointment for three weeks.

"Insect bite hypersensitivity is the most common cause of pruritus (itchiness) in horses, affecting equids in almost all parts of the world," van den Boom said in the study, adding that IBH is an allergic reaction to insect bites. Clinical signs include scratching and rubbing, excoriations (areas where the skin is rubbed off), oozing of serum, patchy alopecia (hair loss), scaling, and hyperkeratosis (callousing).

Van den Boom and his colleagues separated 26 IBH-affectedhorses (ages 3 to 25) into two groups--a case group that would be treated with the phytogenic ointment, which researchers previously confirmed as having anti-inflammatory and healing properties, and a control group that would be treated with the placebo ointment (an unmedicated polyethylene glycol-based ointment) --to determine if a phytogenic ointment would be helpful in treating IBH.

A thin layer of either ointment was applied to open lesions caused by IBH once daily. The horses' owners and the researcher were blinded as to whether the horses were being treated with the phytogenic or the placebo ointment. The lesions were counted, measured, and photographed at the beginning of the study, and then again on Days 7 and 21 of the 21-day study. The horses remained under their owners' care, as the researchers believed the owners would be able to determine whether their horses were more or less comfortable with the trial ointments. All the horses were kept outside during the day and most were kept outside at night as well.

At the conclusion of the study, the researchers noted that the number of lesions in both the test group and the control group that were present on the first day of the study had been reduced by 84% and 92%, respectively. Of the lesions that were noted on Day 7 of the study, the number of lesions in the test group and the control group had been reduced by 89% and 88% respectively. Van den Boom noted that the differences between the groups were not statistically significant.

The average surface area of the lesions present at the beginning of the study was reduced by 75% in the test group and by 90% in the control group by the end of the study. Of the lesions noted at Day 7, the test group's lesions were reduced by 92% and the control group's were reduced by 24%. Again, the researchers noted that the differences between the groups were not statistically significant.

The team noted that both the control and the test groups showed signs of reduced sensitivity to the insect bites throughout the course of treatment; however, the control group horses seemed to show more signs of discomfort, noted researchers.

Van den Boom added that because both groups were treated with an ointment, "it cannot be excluded that the number of lesions and lesion size would have improved without (any) treatment.

"While the ointment does not cure IBH it seems to have a soothing effect on the skin lesions," he said. "Ointments are best used in combination with measures to try to prevent IBH: stabling horses when midges are most active, using insect rugs, and/or insecticides."

The study, "The healing effects of a topical phytogenic ointment on insect bite hypersensitivity lesions in horses," was published in the January 1, 2011, issue of the Netherlands Journal of Veterinary Science. The abstract is available online.

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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